Process of manufacture of alkali-metal sulphides



Patented Aug. 23, 1 927,

-. UNITED STATES PATENT OFFICE,

HORACE FREEMAN, 0F SHAWINIGAN FALIES; QUEBEC, CANADA, ASSIGNOR OF ONE- HALF TO CANADA CARBIDE COMPANY, LIMITED, OF MONTREAL, CANADA.

PROCESS OF MANUFACTURE OF ALKALI-METAL SULPHIDES.

No Drawing. Original application filed February 14, 1923, Serial No. 619,080. Divided and this application filed June '30, 1924. Serial No. 723,135.

This invention is a division from my former application, Serial No. 6191030, filed the 14th day of February, 1923, and relates to improvements in the 'manufacture'of sodium sulphide, and the primaryobject is to obtain a higher yield of an improved prod-' not and in a less time than has heretofore been the case. r

A further object isito overcome the inherent difliciilties in dealing with sodium sulphide arising from its practically infusible nature. v v

A still further object is to render the electric furnace available for this manufacture. The parent application relates broadly to the manufacture of sodium sulphide using other sulphides to produce with the sodium sulphide mixture of sulphides having relatively low melting points. The additional sulphides are identified as those soluble in aqueous solutions of sodium sulphide and particularly potassium sulphide. The present application relates to the use of those sulphides which are insoluble in concentrated aqueous solutions of sodium sulphide, and more particularly to the heavy metal sulphides and certain alkaline earth metal sulphides, namely, calcium and barium sulphides.

At present sodium sulphide is commercially produced by heating to a bright red heat-in a fuel fired furnace, a mixture-of sodium sulphate with a carbonaceous reducingagent,"such as coal or sawdust.-

As sodium sulphate is fusible, and sodium sulphide is not fusible at temperatures which are commercially practicable in this art, it is found that when the proportion of sulphate predominates, as during the earlier stages of the reduction, *the charge remains liquid. When about fifty per cent of sulphide is formed, the mass thickens and becomes more solid; as a consequence the necessary contact between the reacting particles is prevented and-the reduction is checked.

For this reason, the product of this method of operation seldom contains more than sixty-five er cent of sodium sulphide and is obtained rom the furnace in the form'of a .abling the sulphide to semi-solid mass, which is practically 'electrically non-conductive even when hot,

In carrying out this process I have found that the imperfections of this method of production, viz, the-low grade of the fuel fired furnace product and the long period required for the reaction, are due to the infusibilityof sodium sulphide, which also introduces complications in its removal from the furnace. I

An object of this invention is to render the furnace charge fusible throughout the period of operation and in some instances 'at a lower temperature than is generally used for the reduction. The charge being fluid, the reaction is more complete and the yield of sodium sulphide is greater. Also, owing to its fluidity, the charge is electrically conductive enabling use of the electric furnace for heatingv in all stages and further enfurnace. c

I have found that sodium sulphide which, in the pure state, is infusible, or practically so, forms readily fusible compounds when mixed with other sulphides, such as those of potassium, calcium, barium, strontium, copper, zinc, lead, iron, and many others.

During the course of a long investigation of the products so obtained, I have found that the lowering of the fusing point of sodium sulphideis particularly great when potassium sulphide is added to it. Thus, a mixture is proportion of one mole of sodium sulphide 'to' one mole of potassium sulphide melts to a thin. mobile liquid at 420. (1.,

' while the addition of only ten per cent of be tapped from the potassium sulphide to sodium sulphide produces a mixturemelting at 570 C. I

, Furthermore, the double sulphides of sodium with lead, with zinc, with iron and with copper-are very mobile liquids at temperatures much below 700 n 0. Also the double sulphides of sodium with the alkaline' earth metals fuse readily at relatively low temperatures.

Of the alkaline earth metal sulphides, barium sulphide and calcium sulphide have an additional characteristic in common with the heavy metal sulphides, namely, they are till) lid insoluble in concentrated aqueous solutions of sodium sulphide. In this connection it may be noted that iron and barium sulphides are to some extent soluble in very dilute solutions of sodium. sulphide.

In carrying out this process for the production of sodium sulphide the above de scribed properties are made use of in the following manner according to the product it is desired to obtain.

If the product required is hydrated sodium sulphide, free from admixture with other sulphides, the reduction of sodium sulphate is carried out with a reducing agent, such as coal, in the-ordinarymanner, but when or before the previously mentioned thickening of the reacting mass takes place, a proportion of an insoluble sulphide is added. slithcient to make the charge liquefy or to keep the same liquid. A very small proportion of the added sulphide will liquefy the charge at a temperature of 1,000 6., while the addition of a molecular proportion of lead sulphide will cause liquefaction of the sodium sulphide at 550 (3., and when a molecular proportion of zinc sulphide is used, at 620 C.

The common sulphide ores are used for this purpose or refined or recovered sulphides may be used as obtained in the later steps of the process.

The insoluble sulphide may be added to the charge of sulphate and its reducing agent prior to feeding them into the furnace, or it may be added at any subsequent stage in order to bring about the desired result, viz, the maintaining of the sodium sulphide in the reaction mixture in a liquid condition so that reduction may proceed to completion. As an alternative a metal sulphate may be added which will reduce to a sulphide to fuse with the sodium sulphide. v

' During the period of reduction the carbon monoxide gas produced, easily and quietly escapes from the mobile liquid. When the evolution of gas ceases reduction is complete and the charge may be tapped or poured from the furnace.

The product of this operation is sodium sulphide in admixture or combination with guiclrly settles on account of its not objectionable inasmuch as these so 'phides will perform the same function as sodium sulphide in many of its various applications in the arts. 4

As previously stated, potassium sulphide is particularly effective in rendering sodium sulphide fusible in the process of reduction. I

Less than ten per cent of thepotassium sulphide is required and in most cases less than five per cent of the Weight of sodiumsuh phide is a practicable proportion to use, although I do not desire to be confined to any particular proportion.

My process for producing the metal. sulphide consists in heating a mixture of sodium sulphate with the desired .proportion of potassium sulphate and a carbofused alkali naceous reducing agent. Potassium sulphide isformed coincidentally with sodium-sulphide and the charge remains liquid While the reduction is carried to completion. As

an alternative I mayv add previously pre'-' pared potassium sulphide to the sodium sulphate charge undergoing reduction. The

result is the same, i. e.", the liquefaction of the charge. Y

The process may be operated similarly using alkaline earth metal sulphides and mixed with the sodium sulphate.

The product can then be tapped or runfrom the furnace direct into containers for shipping, it ma be cooled in moulds, or itmay be quicklycooled on a rotating watercoolcd drum and produced in the form-of flakes as is now done with caustic soda and with c anid. llfit the process here described the time required for reduction is much shortened and a smaller amount of the reducingiagent is used than in the process heretofore prac-- tised. The reduction is carried much'ifun ther than in the usual process, owing to the mobility of the charge in the furnace and the intimate contact or particles thereby provided.

I do not desire to be confined to any particular form of furnace in carrying out this process, but I prefer and have used an electric furnace for the purpose, utilizing the charge itself as the resistor. The electric furnace is preferred as it. is more economical and avoids oxidation of the sulphide product, which is apt'to take lace in a fuel fired furnace. My process "or the first time makes the electric furnace available for this manufacture, allowing of the tapping of the liquid product and dispensin with the use of moving devices for stirring the charge. 1

In carrying out any of the variations of this process I may either add the desired sulphide or sulphides to the chargefo'r I may, as described, add the corresponding sulphate or sulphates which will be reduced to sulphides coincident with the reduction of sod'ium'sulphate. The product of the process here described contains larger percentages of available sulphide than is atall possible by themethod now commonly used. I Having thus describedmy invention, what I claim is 1. The process of producing sodium 'sul phide which consists in heating sodium sulphate with a carbonaceous reducing agent in the presence of a sulphide insoluble in. concentrated aqueoussolutio'ns of sodium sulphide, whereby the sodium sulphide is maintained molten and freely fluid at atemperature under 1,500 C. v

2. The process of producing sodium sulphide which consists, in fusing sodium sulphate with a heavy metal sulphide in presence of .a carbonaceous reducing agent, whereby the sodium sulphide produced by substantially complete reduction of the sulphate is capable of liquefaction.

3. The process of producing sodium sulphide, which consists in heating sodium sul-' phate with a carbonaceous reducing agent at a temperature under 1,500 C. in the presence of a sulphide insoluble in concentrated aqueous solutions of sodium sulphide, lixiviating the sulphide product with water,-separating the solution of sodium sulphide 'fromthe insoluble sulphide, and crystallizing the sodium'sulphide from the solution.

4. The rocess of producing sodium sulphide, which consists in heating sodium sulphate with a carbonaceous reducing agent in the presence of-a heavy metal sulphide at ;such temperature [that the formed sodium sulphide is maintained molten until after substantially complete reduction of the sodium sulphate is efi'ected, lixiviating the sulphide-product with water, separating the solution of sodium sulphide from the heavy metal sulphide, and crystallizing the sodium sulphide from the solution.

5. In a process for obtaining sodiumsulphide, the procedure which consists in treating with water a solid mixture of sodium sulphide and a sulphide insoluble in concentrated aqueous solutions of sodium sulphide, dissolving the sodium sulphide. separating the solution from the insoluble sulphideand allowing sodium sulphide to .crystallize from the solution. k

6. In a process for obtaining sodium sulphide, the procedure which consists in treating with water a solid mixture of sodlum ofanother metal insoluble in concentrated.

aqueous solutions of sodium sulphide, .by passing an electric current through the charge suflicient-to maintain such temperature that the formed sodium sulphide is maintained molten and electrically conductive until after; substantially complete reduction of the sodium sulphate is e ected.

8. The process of making .sodium sulphide which com rises heating sodium sulphate with a car onaceous reducing agent (and in presence of a heavy metal sulphide in an electric furnace.

9. The product which com rises sodium sulphide fused with a sulphi e of another metal which sulphide is insoluble in aqueous solutions of sodium sulphide, the, sodium sulphide content of the product being upwards of 50%.

10. A process for the substantially complete reduction of sodium sulphate to sodium sulphide, which consists in heating sodium sulphate and a heavy metal sulphide with a carbonaceous reducing agent at a temperature over 1,000 C.

11. A process for the substantially com:

plete reduction of .sodium sulphate to sodium sulphide, which consists in heating sodium sulphate and a metal sulphide insoluble in concentrated aqueous solutions of sodium sulphide with a carbonaceous reducing agent at atemperature'over 1,000 C.-

12. A process for the substantially complete reduction of sodium sulphate to sodium sulphide, which com rises heating sodium sulphate with a carbonaceous reducing agent at a temperature sufficient for reduction and. in presence of a heavy metal sulphide, whereby the sodium sulphide as *it forms is fluxed and maintained molten until molten until after (substantially complete reduction ofthe sul hate.

.14. A. process 0 makingia sodium sulphide product with over 80% sodium sul-- phide content, which comprises fusing toma am gether sodium sulphate and a metal sulphide sodium sulphate with a carbonaceous reduc- Which is insoluble in concentrated aqueous ing agent at a. temperature over 1,000 C. 10 solution of sodium sulphide, in presence of and in presence of a metal sulphide which a carbonaceous reducing agent. is insoluble in concentrated. aqueous solutions 5 15. A process of making a sodium sulphide of sodium sulphide.

product of over 80% sodium sulphide con- In witness whereof, I have hereunto set tent and free from sodium carbonate and my hand. sodium sulphate, which comprises reducing HORACE FREEMAN. 

